Not all adult birds are finicky eaters. I had one hen who converted herself onto a healthier diet and I didn't even try! Well, in her last home she was eating the crappy Walmart bird food, which ended up being the wild bird seed when the people decided to be even cheaper. I don't know what she ate before that home, but I can't imagine it was anything beyond seeds. She had lost her mate in her previous home, and not knowing how old she is, I figured she would be hard to convert to eating healthier.
When I first took her in, all I fed her was seeds. When I introduced her to my flock, she basically made a B-Line for the dish of pellets! Haven't looked back since! There are multiple ways to convert a bird to eating healthier, but one of the best ways is to already have a bird(s) that eats good.
Beyond that, it's just being creative! Trying different ways to convert them to eating healthier! There's a difference between not liking a food and not recognizing something as food. I was born and raised American, but I am 1/8th Filipino. I'm pretty sure I'd have a difficult time eating some of the Filipino cuisine! Or even some of their regular dishes!
For example... Balut! That's one dish I doubt I have the stomach to eat, let alone the heart to!
The food pyramid is good, although every species diet is going to differ some. Conures may require extra vitamin K. Amazons may require extra vitamin A but a diet lower in fat and/or protein. African Greys may require extra vitamin A and calcium (along with vitamin D). Macaws may require a higher fat diet.
It may be a good guideline but one should also be aware of any special dietary requirements of the species that they keep. (not to mention specific birds in their care) It's not really difficult to feed them, though.
